The present invention generally relates to receiver circuits, and more particularly to a receiver circuit which detects a weak signal and amplifies the signal to an amplitude suited for a predetermined signal processing. The receiver circuit according to the present invention is particularly suited for receiving a detection signal which is output from a sensing device such as a computer tomography device.
Recently, there are demands to realize a receiver circuit having a high gain, a wide frequency band and a stable characteristic in response to a detection signal which is weak and has a wide frequency band to suit various environments in which the receiver circuit is used. For this reason, there is a proposed receiver circuit which uses a discrete preamplifier and a general purpose multiplier which are discrete. However, such a proposed receiver circuit is easily affected by a change in the ambient temperature. In other words, the characteristic of the receiver circuit deteriorates and the detection accuracy becomes poor due to the increase in current consumption, and there is a need to stabilize both the characteristic and the detection accuracy of the receiver circuit regardless of the ambient temperature change.
FIG. 1 shows an example of a conventional receiver circuit. A receiver circuit 1 shown in FIG. 1 includes a preamplifier 2 which amplifies an input detection signal from an input terminal 4 to a suitable amplitude, and a general multiplier 3 which gives an arbitrary gain to an amplified output signal of the preamplifier 2 and outputs an amplified detection signal via an output terminal 5. The preamplifier 2 and the general purpose multiplier 3 are discrete. For example, the input detection signal applied to the input terminal 4 is output from a computer tomography device (not shown).
When the preamplifier 2 receives a weak detection signal, the preamplifier 2 amplifies the weak detection signal to a suitable amplitude which can be processed in the general purpose multiplier 3. Hence, the general purpose multiplier 3 amplifies the output signal of the preamplifier 2 with the arbitrary gain so as to obtain the output detection signal which has a desired amplitude.
However, the receiver circuit 1 is a simple combination of the preamplifier 2 and the general purpose multiplier 3 which are discrete. As a result, the temperature characteristics of the preamplifier 2 and the general purpose multiplier 3 do not match, and consequently, the characteristic of the receiver circuit 1 deteriorates and the current consumption increases. In other words, when the ambient temperature changes, there are problems in that the operation of the receiver circuit 1 becomes unstable, the detection accuracy especially with respect to the weak signal becomes poor and the power consumption of the receiver circuit 1 increases.
That is, when the receiver circuit 1 is simply designed from the preamplifier 2 and the general purpose multiplier 3, the current consumption of the receiver circuit 1 changes because the receiver circuit 1 as a whole has a temperature characteristic. For this reason, when the receiver circuit 1 is connected within a system, the system must have a power source which can cope with the change in the current consumption of the receiver circuit 1. For example, in a case where the power source of the system only has a capacity sufficient to drive the receiver circuit 1 at room temperature when the current consumption is relatively small, the characteristic of the receiver circuit 1 deteriorates when the current consumption increases because the power source of the system can no longer satisfactorily drive the receiver circuit 1.